To get to a point where people can begin to group together into communities, they need to survive the die off.
If something dramatic ever happens, like grid down for six months to a year, then there will be deaths running into the millions. There simply isn't enough capacity to FEED everyone without the mega farms and serious transportation infrastructure.
The survivors will be those that have supplies (and hold onto them) or find SOME way to scrape by until the population pressure is low enough to begin trusting again.
Since none of us know what that drama might actually BE, you plan for what could reasonably happen, that you have a chance of surviving.
Mega Quake with tsunami that wipes out everything within 75 miles of the eastern seaboard? Sorry. None of us are going to make it. That power outage? Maybe, depending on what you stored. Super virus? Luck of the draw. Zombies? I just have to run faster than you.